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Colorectal Cancer Prevention (PDQ®): Prevention - Health Professional Information [NCI] - Overview



Based on solid evidence, harms of postmenopausal combined estrogen plus progestin hormone use include increased risk of breast cancer, coronary heart disease, and thromboembolic events.

Magnitude of Effect: The WHI showed a 26% increase in invasive breast cancer in the combined hormone group, a 29% increase in coronary heart disease events, a 41% increase in stroke rates, and a twofold higher rate of thromboembolic events.

Study Design: Evidence from RCTs.
Internal Validity: Good.
Consistency: Good.
External Validity: Fair.

Polyp removal


Based on fair evidence, removal of adenomatous polyps reduces the risk of CRC. Much of this reduction likely comes from removal of large (i.e., >1.0 cm) polyps, while the benefit of removing smaller polyps—which are much more common—is unknown. Some but not all observational evidence indicates that this reduction may be greater for left-sided CRC than for right-sided CRC.[24,25,26]

Magnitude of Effect: Unknown, probably greater for larger polyps (i.e., >1.0 cm) than smaller ones.

Study Design: Evidence obtained from cohort studies and one RCT of sigmoidoscopy.[25]
Internal Validity: Good.
Consistency: Consistent.
External Validity: Good.


Based on solid evidence, the major harms of polyp removal include perforation of the colon and bleeding.

Magnitude of Effect: Seven to nine events per 1,000 procedures.

Study Design: Evidence from retrospective cohort studies.[29,30]
Internal Validity: Good.
Consistency: Good.
External Validity: Good.

Diet modification

A diet low in fat and meat and high in fiber, fruits, and vegetables


Based on fair evidence, a diet low in fat and meat and high in fiber, fruits, and vegetables started as an adult does not reduce the risk of CRC by a clinically important degree.

Study Design: Evidence obtained from pooled analyses of multiple cohort studies and RCTs.
Internal Validity: Fair, but measurement error is a potential problem.
Consistency: Some inconsistency, with one large pooled study [31] finding a reduced risk of distal colon cancer associated with fruit and vegetable intake. RCTs have been consistent.
External Validity: Good, studies have included large population-based studies.


There are no known harms from dietary modification, including reduction of fatty acids or meats and an increase in the intake of fiber, fruits, and vegetables.

Study Design: Cohort and RCT's.
Internal Validity: Good.
Consistency: Good.
External Validity: Good.

Calcium supplementation


The evidence is inadequate to determine whether calcium supplementation reduces the risk of CRC.

Study Design: Pooled and individual prospective cohort studies, meta-analysis of three RCTs with adenoma recurrence as an outcome, and one large individual RCT in women with CRC as an outcome.
Internal Validity: Good.
Consistency: Poor; the RCT with CRC as an outcome [32] found no reduction in CRC incidence, while prospective cohort studies found a reduction in CRC incidence between high and low calcium groups; three RCTs found a reduction in adenoma recurrence with calcium supplementation.[33]
External Validity: N/A.

WebMD Public Information from the National Cancer Institute

Last Updated: February 25, 2014
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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